Teens who exhibit a circadian tendency toward eveningness ('night-owls') follow a delayed sleep schedule, increasing activity later in the day and both going to sleep and getting up later, compared to morning-types ('larks'). The circadian tendency toward eveningness during adolescence arises from a confluence of psychosocial, behavioral and biological factors and is an important contributor to, and maybe even cause of, vicious cycles that escalate vulnerability and risk for poor health and major forms of psychopathology. Indeed, an evening circadian tendency has been associated with a wide range of adverse effects including poorer health, poorer academic performance, poorer self-regulation, greater use of substances, greater tendency for impulsivity, more depression and anxiety, greater emotional instability and more aggressive and antisocial behavior. While the biological shift toward eveningness during puberty may be difficult to modify, the psychosocial and behavioral contributors are modifiable. Moreover, modifying these contributors will eliminate key factors that exacerbate the biological shift. The proposed research will advance current knowledge on the role of eveningness as a mechanism contributing to poorer outcomes during adolescence. We aim to reduce eveningness among 10-18 year olds via an innovative intervention; the BRIGHT intervention (Biological Rhythm Intervention for Growing Healthy Teens) which integrates evidence-based treatments derived from basic research on the circadian system. We will randomly allocate adolescents with an evening circadian tendency, and who are 'at risk' in at least one of five health domains (emotional, cognitive, behavioral, social, physical), to either: (a) BRIGHT (n = 86) or (b) Psychoeducation (n = 86). Measures will be taken pre-treatment, post-treatment, and at 6 and 12 months post-treatment. The hypothesis to be tested is that BRIGHT, relative to Psychoeducation, will be associated with improvement in sleep and the five health-relevant domains at the end of treatment and that these gains will be maintained 6 and 12 months later. Planned secondary analyses include an evaluation of the effects of BRIGHT, relative to Psychoeducation, on change to an earlier endogenous circadian phase and change in the timing and intensity of light exposure. Mediation analyses will examine whether improved sleep or a change in the timing of light exposure contributes to reduced risk in the five health domains. Moderation analyses of variation in intervention effect due to baseline demographics (gender, age, pubertal status), baseline sleep and other risk measures will also be evaluated. Multiple methods include self report, ecological momentary assessment, behavioral tasks and biologic measures. Multiple informers include youth, parent/s and teacher. This research is a first step within a longer term plan to accelerate knowledge on the potentially powerful positive effects, for the developing neural system, of simple, disseminable psychosocial interventions specifically designed to target modifiable risk factors across adolescence.